Sanding stair treads + 3 coats of varnish - refurbishing existing

Sanding and revarnishing makes sense when the damage is mainly on the surface. Before any work starts, walk up and down the stairs and put your weight on each tread. Sanding will not fix creaking, a tread that moves underfoot or a loose handrail.

Refurbishing is a good fit when:

• The treads and strings are firm and nothing moves
• The wood shows no signs of woodworm or rot
• The damage only goes through the varnish and a thin top layer of wood

Deep cracks in load-bearing parts, loose fixings into the wall or treads damaged well below the surface are a reason to consider replacing individual treads. The thickness of the top wood layer matters too. Some stairs only have a thin veneer of solid wood on chipboard or a laminated core. You can sand these only very carefully, and sometimes not at all. You can usually see the thickness on the side edge of the tread or from underneath the staircase.

The process is much the same for most wooden stairs. What changes is the number of sanding passes and the type of varnish.

1. Inspection and preparation. The tradesperson checks that the treads are firm, removes any trims and covers that are in the way, and protects the surroundings with sheeting and tape.
2. Coarse sanding. A coarse abrasive takes off all the old varnish and levels out the worn areas. A belt or random orbital sander does the flat surfaces. A detail sander or hand sanding deals with corners, edges and spots next to the balustrade.
3. Fine sanding. The grit gets finer step by step, so the scratches from coarse sanding disappear and the grain shows through.
4. Filling. Small cracks and dents are filled with a wood filler that matches the timber and suits the chosen varnish. Once dry, the filled spots are sanded flush.
5. Removing dust. The dust is vacuumed and the surface wiped with a slightly damp cloth. Any dust left behind gets trapped in the varnish and stays visible.
6. First coat. This is often a primer or sealer coat. It seals the wood and helps the next coats bond.
7. Light sanding between coats and two more coats. Once each coat is dry, the surface is lightly sanded with fine abrasive and dusted off, and the next coat goes on.

The varnish manufacturer sets the drying times between coats, and the temperature and humidity in the room affect them. A typical water-based varnish usually needs a few hours, but full curing takes considerably longer.

Stairs need a floor varnish, not a furniture varnish. Stairs take more wear than a living room floor, because everyone steps on the same spots every day. Polyurethane varnishes are the usual choice because they stand up well to abrasion.

• Water-based varnishes smell less, dry faster and yellow the wood less. They are the usual choice in a house people are living in.
• Solvent-based varnishes can bring out the colour and grain more strongly, but they smell strongly. They need good ventilation and no naked flames nearby.
• Sheen level is a matter of taste. Matt and satin finishes hide small scratches better. Gloss looks more striking, but every mark shows.

Why three coats? A single coat is thin and soon wears through. Three coats with light sanding in between build a continuous film. This protects the wood from wear and from damp off shoes, and it lasts longer before the next refurbishment. Oil is sometimes used on stairs instead, but it needs more frequent maintenance.

How much work and time the job takes depends mainly on:

• The number and width of the treads, and whether the risers are sanded too
• The shape of the staircase, since winders and turns take longer than straight flights
• The type of wood, since hard oak or beech takes longer to sand than spruce or pine
• The type and thickness of the old finish, as some older varnishes clog the abrasive
• How deep the worn areas are and how many spots need filling
• Balusters and newel posts set directly into the treads, which have to be sanded around by hand

The job gets easier when the stairs are clear, with no carpet runners or stuck-on anti-slip strips whose adhesive has to be removed first.

With patience and the right hired sanders, you can do this refurbishment yourself. Expect a lot of dust. Wear at least an FFP2 respirator and eye protection. If you live in a flat, for example a maisonette, ask the building management or owners' association what hours noisy work is allowed.

1. Check that the treads are firm and how thick the solid wood is.
2. Remove trims, stair mats and any adhesive residue.
3. Cover the surroundings, the balustrade and the adjoining floor.
4. Sand off the old varnish with a coarse abrasive down to bare wood.
5. Sand the edges and corners with a detail sander or by hand.
6. Sand the surface with a finer grit, following the grain.
7. Fill any cracks and sand them flush once dry.
8. Vacuum the dust and wipe the surface with a slightly damp cloth.
9. Apply the first coat of varnish thinly and evenly.
10. Once dry, sand lightly and remove the dust.
11. Apply the second and third coats the same way.
12. Let the varnish cure as the manufacturer instructs, and use the stairs gently until then.

If you need to use the stairs while the work is going on, varnish every other tread first and do the rest once those are dry. This does make the job take longer.

• Leftover patches of old varnish. New varnish bonds poorly to them, blotches appear and it peels later on.
• Uneven sanding. Skipping a grit or pressing too hard in one spot leaves waves and hollows, and the varnish makes them stand out even more.
• Sanding through a veneer or an edge. With a thin top layer, a moment's inattention is enough for the core to show through.
• Skipping the sanding between coats. The coats bond less well to each other and the surface feels rough with dust.
• Furniture varnish instead of floor varnish. It looks good for a short time, then quickly wears off where people step.
• Using the stairs too soon. Walking on the stairs in shoes before the varnish has cured leaves marks in it.

When the work is handed over, look at the stairs in daylight, and also at a low angle against the window. This shows up unevenness that you miss when looking straight down.

• The varnish has the same sheen on every tread, with no dull or shiny patches
• The surface has no roller marks, runs, trapped hairs or dust
• The nosings are smooth and the core does not show through anywhere
• Filled spots match the wood in colour and cannot be felt with a finger
• Corners by the wall and around the balusters are sanded and varnished
• Surrounding walls, floor and balustrade are clean, with no varnish marks
• You know which varnish was used and when the stairs can take full use